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Andy Revkin of the NYT recently posted at his “Dot Earth” blog an update by a scientist to the effect that apparently the increasing summer melt in Greenland is not markedly lubricating glacier flow. While this doesn’t alter the fact that the Greenland melt (and outlet glaciers)continues to accelerate, it does abate some concerns that the thawing Greenland ice sheet could make a very rapid contribution to rising sea levels by more quickly offloading icebergs.

The core issue for policymakers is not whether global warming is affecting the Greenland ice sheet (of course it is), nor even whether the Greenland is in negative mass balance and contributing to sea level rise (it is). Rather, the key question is whether half the ice sheet is in danger of breaking off and sliding into the sea, as Al Gore warned in An Inconvenient Truth.

In AIT, Gore presented as a serious scientific possibility the simultaneous crackup of the Greenland and West Antarctic ice sheets. That would raise sea levels 18 to 20 feet, with the consequence, Gore said, that 100 million people would “be displaced,” “forced to move,” and “have to be evacuated.”

Gore and his allies seek the political power to reprogram the U.S. and global economies. To justify this risky experiment, they depict global warming as a “planetary emergency, a crisis threatening the survival of civilization and the habitability of the Earth.” They claim to speak for the “consensus of scientists,” but what they actually present is science fiction. No child should go to bed worrying about a 20-foot wall of water sweeping across the globe. Neither should the child’s parents.

(emphasis added)

With this, Marlo deftly misstates the core issue for policy makers, distracts us from what scientists have long stated are the much greater risks posed in Antarctica, shifts our attention from the risks that our unmanaged activities are posing to the risks that Al Gore (and others who believe policy changes are needed) is posing and raises a strawman disaster scenario. With slick work like this, maybe the folks backing Gore’s climate publicity campaign should consider making substantial contributions that could bring CEI over to his side!

Allow me to elaborate a bit (based on comments I posted on the same Dot Earth thread).

1. ML: “the key question is whether half the ice sheet is in danger of breaking off and sliding into the sea, as Al Gore warned”

I strongly disagree. The chief question is whether the existing and growing GHG forcing and albedo feedbacks will COMMIT us to a rapid pulse of ice sheet melting on scales that we can see in the paleo record: several meters per century for a few centuries (for forcings smaller than the BAU scenario). This possibility was noted back in 1978, and all we’ve seen since then is an accelerating expansion of melt areas and mass loss. If such a melt pulse is in the cards, related questions are how to deal with the rising sea levels (both the continued shift of cities and infrastructure and the related losses, costs and upheaval) and whether mitigation efforts can head off or materially slow such a melting.

Presumably Lewis is aware, as Jim Hansen and other climate scientists have been making this point frequently, that the models of ice loss reviewed by the IPCC simply don’t include the mechanisms for such actual, rapid ice loss, and so probably underproject the loss that we are likely to see this century. In fact, as well, we have seen net mass loss in the West Antarctic Ice Sheet (WAIS) due to melting and calving, despite expectations in the IPCC that increased snowfalls brought by warming temperatures would result in WAIS gaining mass.

2. ML: “In AIT, Gore presented as a serious scientific possibility the simultaneous crackup of the Greenland and West Antarctic ice sheets. That would raise sea levels 18 to 20 feet, with the consequence, Gore said, that 100 million people would “be displaced,” “forced to move,” and “have to be evacuated.” The recent Science study exposes Gore’s doomsday scenario (or half of it, anyway) as unscientific.”

If Gore referred to a rapid loss of the Greenland Ice Sheet, he was not reflecting scientists’ concerns (other than the concern for a geologically rapid melting over centuries), because Greenland’s ice is all on land and cannot simply collapse into the ocean. However, that is NOT true of the WAIS, which is not walled in, much of it sits on land that is actually below sea level and can quickly lose mass into the sea, and is at present held back only floating ice sheets that are now rapidly crumbling. There is significant scientific literature on this point, and a significant increase in alarm just over the past few years. The WAIS is now referred to as an “awakening giant”. Gore is right that scientists are concerned that the WAIS may rapidly lose mass into the sea – rather quickly raising sea levels by 12 to 18 feet – that scientists believe that human activities have kicked off a number of changes in Antarctica, and that scientists believe AGW may also initiate and accelerate the collapse of the WAIS.

It is a puzzle that Lewis does not mention these concerns, as he appears to be well aware of them. In own his paper criticizing AIT, Lewis specifically noted that the process of retreat in glaciers such as WAIS whose base is below sea level, once initiated, “cannot be stopped”. Lewis quoted one scientific paper as follows:

“Increased pressure at these greater depths lowers the melting point of this ice, increasing the melting efficiency of the warmer water. Rapid melting results.”

“Retreating glaciers lengthen the distance warmer water must travel from any sill to the grounding line, and eventually tidewater glaciers retreat to beds above sea level. This might limit the retreat in Greenland but will save neither West Antarctica, nor the equally large subglacial basin in East Antarctica where submarine beds extend to the center of the ice sheet.”

Here are links to just a few of the discussions by scientists of WAIS:

3. ML: “Gore and his allies seek the political power to reprogram the U.S. and global economies. To justify this risky experiment, they depict global warming as a “planetary emergency, a crisis threatening the survival of civilization and the habitability of the Earth.”

Certainly there are risks associated with the climate strategy being offered by Mr. Gore, as well as with any kind of climate strategy – including doing nothing. We should certainly evaluate the comparative benerfits, costs and risks of all policy options. But Mr. Lewis instead offers us loaded statements. There are equally honest ways to rephrase these loaded statements. For fun, I offer the following to Mr. Lewis:

“You and your allies (fuel producers and consumers) seek to use political power to protect the benefits accruing to you as a result of the failure of market economies to require you to bear the full costs and risks generated by your economic activities, so that you reap gains while shifting those costs and risks to others. To justify continuing with this risky experiment with the Earth’s climate, you depict Gore as being on an unhinged, yet hypocritical and cunning Jeremiad, downplay the risks that even Exxon says merit present action, and paint everyone who agrees with them – from the world’s scientific bodies and major investors to Pope Benedict – as part of a cabal or cult of irrational believers or as malevolent man-haters out to poison our precious bodily fluids/destroy the market system itself, while you decline to straightforwardly address obvious externalities, risks or policy options.”

Just how seriously does Mr. Lewis want us to take him?

4. ML: “They claim to speak for the “consensus of scientists,” but what they actually present is science fiction. No child should go to bed worrying about a 20-foot wall of water sweeping across the globe.”

I’ve seen no reference by Gore or other “alarmists” to a “20-foot wall of water” – that appears to be a boogeyman only of Mr. Lewis’s imaginings. However, it is clear that scientists are indeed very concerned about a fairly rapid collapse of the WAIS. This is NOT “science fiction”, as Mr. Lewis would have it.

And maybe Mr. Lewis doesn’t want to worry about it, but Lloyd’s of London certainly is, and is recommending that others worry about it too. A recent report by Lloyd’s on various climate change risks concluded the following regarding the WAIS and Greenland:

It is our view that there are clear and worrying trends in the behaviour of component parts of the Greenland and Antarctic Ice Sheet, with the WAIS in particular showing anomalous behaviour.Meaningful predictions of the likelihood of rapid, catastrophic ice discharge, ice sheet collapse or lake outbursts in the near future are impossible. However, an increase in instability, with a resultant impact on sea level within our lifetime, is a credible risk.

Insurers and other commercial institutions sensitive to these risks should keep a close watch on future developments and be prepared to revise their strategies regularly.

The rest of the report also offers useful analyses. But who wants to read this kind of stuff? Thanks, Mario, for distracting us.

“West Antarctic and Greenland ice sheets are vulnerable to even small additional warming. These two-mile-thick behemoths respond slowly at first, but if disintegration gets well underway it will become unstoppable. Debate among scientists is only about how much sea level would rise by a given date. In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely this century. Hundreds of millions of people would become refugees. No stable shoreline would be reestablished in any time frame that humanity can conceive.”

http://arxiv.org/ftp/arxiv/papers/0804/0804.1126.pdf“Present-day observations of Greenland and Antarctica show increasing surface melt [35], loss of buttressing ice shelves [36], accelerating ice streams [37], and increasing overall mass loss [38]. These rapid changes do not occur in existing ice sheet models, which are missing critical physics of ice sheet disintegration [39]. Sea level changes of several meters per century occur in the paleoclimate record [32, 33], in response to forcings slower and weaker than the present human-made forcing. It seems likely that large ice sheet response will occur within centuries, if human-made forcings continue to increase. Once ice sheet disintegration is underway, decadal changes of sea level may be substantial.

http://www.columbia.edu/~jeh1/2007/Testimony_20070426.p df“One thing that the paleoclimate record shows us is that ice sheet disintegration and sea level rise are usually much more rapid than the opposite process of ice sheet growth and sea level fall. This is reasonable because ice sheet disintegration is a wet process with many positive feedbacks, so it can proceed more rapidly than ice sheet growth, which is limited by the snowfall rate in cold, usually dry, places. At the end of the last ice age sea level rose more than 100 m in less than 10,000 years, thus more than 1 m per century on average. At times during this deglaciation, sea level rose as fast as 4-5 m per century.”

–“The first principle is that you must not fool yourself – and you are the easiest person to fool.”Richard Feynman